Process for treating lead oxidized ores



Patented Dec. 24, 1940 PROCESS FOR TREATING LEAD oxmrznn onus EdwardEisenhauer, In, Los Angeles, Calif.

No Drawing.

6 Claims.

This invention relates to a process for the recovery of themetallicvalues froin oxidized lead ores, such as the lead carbonates.

Lead carbonates such as cerussite are abundant in nature but therecovery of the metallic values therefrom 111.; never been commerciallysuccessful. Attempts have been made to make a mechanical recovery of thevalues by jigging and wet and dry table concentration. These attemptshave not been a commercial success for the oxidized lead, gold andsilver content disintegrates and slimes badly and passes readily withthe water to the tailings. Attempts at direct flotation have likewisenot been successful due to the fact that the oxidized lead wets asreadily as the gangueand will not float. The zinc that is always presentin such ores makes smelting of the ores an expensive procedure.

The principal object of this invention is to provide a commerciallysuccessful process for recovering the metallic values, such as gold,silver and lead, from oxidized lead ores.

Other objects are to provide a process which will require only the usualequipment of an ordi ores of the lead carbonate varieties, such as'ceruss'lte, but it is not, of course, limited to these particular oresas it will be found valuable for the recovery of metallic. values fromother oxidized ores. Cerussite is a lead carbonate ore having thegeneral formula PbCOs, but may also carry commercial values of gold,silver, and cop per in addition to the lead and usually carries smallpercentages of undesirable zinc.

The essence of the invention is the provision ofa simple and highlyeflicient process which will render,the desired metallic values amenableto recovery by flotation. In their natural state, the oxidized metals inthe ore absorb the water in a flotation cell to form a thick mud orslime which quickly settles and which cannot be floated. Attempts havebeen made to convert the oxides to floatable sulphides prior to flotaion but these attempts have not been commercially successful due toinability, without prohibitive expense, to

Application May 16, Serial No. 273,945

nary concentrating mill so that mill investment obtain a completeconversion of all values to sulphides. With this process, however, 95%recoveries have been cheaply made on ores which under the best and mostexpensive prior processes have never run over recovery. 5

Briefly, this invention contemplates the forma tion of nascent HzS gasin the interstices of the pulp body during the time the pulp s beingsubjected to the violent pounding, crushing and grinding action of aball mill or other mechani- 10 cal crushing and comminuting machine.Treatment of the ore with HzS from an outside source would notaccomplish the same result for the nascent state of the gaspersists-only for a matter of seconds after its formation and '15applied gas would therefore not have the great? amnity for the metalsnecessary for a complete conversion, nor could, it be sufllcientlydispersed throughout the mass to contact all particles.

Treatment of the ore with hydrogen-sulphide 20 forming materialsindependent of the grinding or crushing step would not attain the sameefflcient results since the violent crushing and pounding at the exactinstant the gas is formed is necessary to compress the cells and inerstices 25 in the pulp and drive the gas into the interior ofthe-disintegrating particles where it willintimately contact eachmicroscopic metallic grain. However, by forming the gas within all theminute cellular spaces in the pulp and then in- 30 stantly pounding andcrushing. the pulp before It can, however,

the gas leaves its active nascent state so as to drive it into theinternal cellular structure of the grains and particles, we intimatelycontact every moleculeof metal with a gas which is at that '35 instantin its most active condition. 1

In carrying out the process, a soluble sulphide,

such as sodium sulphide, and a soluble reaction agent to liberate HaStherefrom are independently fed to a ball mill or other grinding appara-4o tus simultaneously with the supply of ore thereto. The' ore ispreferably supplied as a 40% wet pulp.

be fed dry and suflicient water added in the mill to bring the contentsto a substantially 40% wet pulp. The two sulphidizing 45 agents and theore pulp are thoroughly intermixed by the violent action of the mill sothat the two agents will be brought together while in widely dispersedcondition throughout the pulp. This causes a uniform formation of H28through-' 50 out the entire pulp mass in intimate contact with theoxidized metallic particles therein. The nascent gas instantly andcompletely converts the oxides of the metals present to sulphides. Thereis undoubtedly a secondary conversion directly between the sodiumsulphide and the ore and it appears that the additional HzS. presentacts as a catalyst to facilitate this secondary action, for resultsattained by the addition of the second HzS forming agent are far inexcess of the results attained by the use of the sulphide alone. n o

Experience indicates that not less than 7 pounds of sodium sulphide,NazS, and not less 1 than 1 /2 pounds of a second reagent per ton or oreshould be used. The second reagent may be any suitable acid'soluble oracid salt which will combine with the sulphide to liberate HzS such assodium bicarbonate, NaHCOs, or sodium acid sulphate, Nail-I804. Thelatter reagent due to its high acid content gives a faster action thanthe bicarbonate and it is preferred on low lime content ores. 1 On oreshaving a high lime content however, the acid action of the sodium acidesulphate is neutralized by the lime and the use of the bicarbonate ispreferred since the latter salt reacts with the lime so slowly that theobjects of the invention are completed before any interference can takeplace.

With the-bicarbonate the reaction is: Na2S+2NaHCO3 =2NmCO3+H2S With thesodiumacid sulphate the reaction is:

Na zS+2NaHSO 4=2NazSO4+I-I2S The reaction of the hydrogen sulphide onthe oxidized lead in the ore is:

5 and a similar reaction takes place with the other metallic valuespresent, with the exception perhalls of the zinc. The carbon dioxide isevolved from the ore in the ball mill or crusher.

If ores of an exceedingly. high lime content 40 are encountered, it isadvisable to employ an ammonium salt, such as ammonium chloride, as thesecond reagent. Very high extractions have been obtained from its It isbelieved that this is due to the fact t at the ammonium chloride,

NH4C1, unites with the sodium hydroxide, formed by the decomposition orthe sodium sulphide in water, to form ammonia gas, NHs,

From the grinding and sulphidizing step the pulp is fed directly toflotation cells where it is floated with any of the standard flotationand frothing reagents as is usual with sulphide ores. The resultingconcentrate is ready for shipment or smelting.

Most, if not all, lead carbonate ores carry traces of zinc which ifallowed to remain in the flnal concentrate interfere with smelting. Thisprocess appears to automatically remove the vexatious zinc problem forno zinc appears in the concentrate from the flotation cells. 1

Perhaps this is due to the fact that the zinc is not converted to thesulphide under the conditions present in the grinding mill, or perhapsthe sulphide, it formed at all, is not stable, or perhaps it forms tooslowly to be completed in the short time interval in the mill. However,it does appear that an automatic classification and elimination of thezinc from the other metals present is obtained by this process.

While a specific process has been described herein it is desired to beunderstood that the same may be varied within the scope of-the claimswithout departing from the spirit of the invention.

I claim:

1. A process for treating oxidized ore for the recovery of the metallicvalues therefrom comprising: feeding said ore to a wet ball mill;simultaneously feeding sodium sulphide and sodium bicarbonate to saidmill; grinding the mixture to a pulp; thence treating the resulting pulpby flotation to recover the metallic values therefrom.

2. A process for treating oxidized ore for the recovery of the metallicvalues therefrom comto a pulp; thence treating the pulp by flotation torecover the resulting metallic sulphides therefrom.

4. A method of sulphidizing oxidized ores prior to flotation comprising:admixing dry sodium acid sulphate and dry sodium sulphide with saidores; thence grinding the mixture together in the presence of moisture.

5. A method of sulphidizing oxidized ores prior to flotation comprising:adding dry sodium bicarbonate and dry sodium sulphide to said ores;

, thence grinding the mixture together in the presence of moisture.

6. A method of sulphidizing oxidized ores prior to flotation comprising:admixing dry sodium sulphide and a dry ammonium salt with said ores;thence grinding the mixture in the presenceof moisture to form nascentammonium sulphide and ammonia in the interstices of said ore; thencesubjecting said ore to flotation.

EISENHAUER, J R.

